Image sensors and methods of operating the same

ABSTRACT

An image sensor includes a pixel array of pixels arranged in one or more rows and one or more columns, the pixel array configured to generate an image based on light being incident on one or more pixels of the pixel array. The image sensor includes pixel load circuitry connected to one column of pixels and including transistors serially connected to each other. The image sensor includes switches connected in parallel to separate, respective nodes between adjacent transistors. The image sensor includes image sensor processing circuitry configured to receive, from image processor circuitry, gain information indicating an intensity of light concurrently with an image being generated by the image sensor, and control at least one switch of the plurality of switches to be turned on/off to change an electrical path of a current that passes through the pixel load circuitry, based on the gain information.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No.10-2019-0010663, filed on Jan. 28, 2019, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

BACKGROUND

The inventive concepts relate to image sensors, and more particularly,to image sensors that fluidly adjust transconductance of a pixel load,and methods of operating the image sensors.

Image sensors can include a pixel array including a plurality of pixels,each pixel including an optoelectronic conversion device (for example, aphotodiode). The pixel array can output (“generate”) an electricalsignal based on using electrons being generated according to theintensity of sensed light that is incident on the pixel array. To form asingle image, respective electrical signals generated by the pluralityof pixels may be generated and collected.

Electrons generated by an optoelectronic conversion device may obtain(“generate”) thermal energy according to an ambient temperature, andkinetic energy of the electrons may increase. Electrons that randomlyvibrate according to the increased kinetic energy may cause thermalnoise in an image sensor that includes the optoelectronic device.

SUMMARY

The inventive concepts provide image sensors that fluidly adjusttransconductance values of pixel loads by controlling a plurality ofswitches, and methods of operating the image sensors. Such image sensorsmay have reduced thermal noise in the pixels of the image sensors as aresult and thus may have improved performance in generating images withimproved resolution due to the reduction of thermal noise.

The inventive concepts also provide image sensors configured to reducethermal noise associated therewith based on changing a transconductancevalue of a pixel load, based on a gain of an image, and methods ofoperating the image sensors.

According to an aspect of the inventive concepts, there is provided animage sensor including a pixel array including a plurality of pixels,the plurality of pixels arranged in one or more rows of pixels and oneor more columns of pixels, the pixel array configured to generate animage based on light being incident to one or more pixels of theplurality of pixels; pixel load circuitry connected to one column ofpixels of the one or more columns of pixels, the pixel load circuitryincluding a plurality of transistors serially connected to each other;and a plurality of switches connected in parallel to separate,respective nodes between adjacent transistors of the plurality oftransistors, wherein the image sensor includes image sensor processingcircuitry configured to receive, from image processor circuitry, gaininformation indicating an intensity of the light concurrently with thepixel array generating the image, and control at least one switch of theplurality of switches to be turned on/off to change an electrical pathof a current that passes through the pixel load circuitry based on thepixel array generating the image, based on the received gaininformation.

According to another aspect of the inventive concepts, there is provideda method of operating an image sensor, the method including receiving,from image processor circuitry, gain information indicating an intensityof light concurrently with generation of an image at a pixel array of animage sensor based on the light being incident to one or more pixels ofpixel array; and controlling at least one switch of a plurality ofswitches of the image sensor to be turned on/off to change an electricalpath of a current that passes through pixel load circuitry of the imagesensor based on the pixel array generating the image, based on the gaininformation, wherein the plurality of switches are connected in parallelto separate, respective nodes between adjacent transistors among aplurality of transistors of the pixel load that are serially connectedto each other.

According to some example embodiments, an electronic device may includeimage processor circuitry and an image sensor, wherein the imageprocessor circuitry is configured to transmit, to the image sensor, gaininformation indicating an intensity of light concurrently with the imagesensor generating an image at a pixel array of the image sensor based onthe light being incident to one or more pixels of pixel array, and theimage sensor includes image sensor processing circuitry configured tocontrol at least one switch of a plurality of switches to be turnedon/off to change an electrical path of a current that passes throughpixel load circuitry of the image sensor based on the pixel arraygenerating the image, based on the gain information.

BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments of the inventive concepts will be more clearlyunderstood from the following detailed description taken in conjunctionwith the accompanying drawings in which:

FIG. 1 is a block diagram of an image processing system according tosome example embodiments of the inventive concepts;

FIG. 2 is a block diagram of a structure of an image sensor according tosome example embodiments of the inventive concepts;

FIG. 3 is an analog circuit diagram illustrating a pixel and a pixelload according to some example embodiments of the inventive concepts;

FIG. 4 is a flowchart of an operation of an image sensor according tosome example embodiments of the inventive concepts;

FIG. 5 is a flowchart of a method of controlling an on/off operation ofa switch, according to some example embodiments of the inventiveconcepts;

FIG. 6A is a circuit diagram illustrating a flow of a pixel load currentaccording to control of a switch to be turned on/off, when a gain valuenot exceeding the first threshold value is received, according to someexample embodiments of the inventive concepts;

FIG. 6B is a circuit diagram illustrating a flow of a pixel load currentaccording to control of a switch to be turned on/off, when a gain valueexceeding the first threshold value and not exceeding the secondthreshold value is received, according to some example embodiments ofthe inventive concepts;

FIG. 6C is a circuit diagram illustrating a flow of a pixel load currentaccording to control of a switch to be turned on/off, when a gain valueexceeding the second threshold value is received, according to someexample embodiments of the inventive concepts; and

FIG. 7 is a block diagram of a computing system including an imagesensor according to some example embodiments of the inventive concepts.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 is a block diagram of an image processing system 1 according tosome example embodiments of the inventive concepts.

Referring to FIG. 1, the image processing system 1 may include an imageprocessor 100 and an image sensor 200. The image processor 100, whichmay also be referred to as “image processor circuitry”, may includeprocessing circuitry such as hardware including logic circuits; ahardware/software combination such as a processor executing software; ora combination thereof. For example, the processing circuitry morespecifically may include, but is not limited to, a central processingunit (CPU), an arithmetic logic unit (ALU), a digital signal processor,a microcomputer, a field programmable gate array (FPGA), aSystem-on-Chip (SoC), a programmable logic unit, a microprocessor,application-specific integrated circuit (ASIC), etc. The image processorcircuitry may include a memory storing a program of instructions andprocessing circuitry configured to execute the program of instructionsto implement the functionality of some or all of the image processor100, including some or all of the sensor control circuit 110, automaticgain controller 120, and digital signal processing circuit 130. Theimage processing system 1 may be included in an electronic device thatincludes the image processor 100 and the image sensor 200. The imageprocessor 100 and the image sensor 200 may be configured to obtain(“generate”) a still image of a subject by transmitting or receiving acontrol signal and image data.

According to some example embodiments, the image processor 100 mayinclude a sensor control circuit 110, an automatic gain controller 120,and a digital signal processing circuit 130. In some exampleembodiments, one or more elements of the sensor control circuit 110,automatic gain controller 120, and digital signal processing circuit 130may be implemented by processing circuitry, such as described above asbeing included in the image processor 100, executing a program ofinstructions stored on a memory device and/or storage device.

The sensor control circuit 110 may control operations of the imagesensor 200. For example, the sensor control circuit 110 may transmit acontrol signal to a control register 210 included in the image sensor200. In response to receiving the control signal, the control register210 may control a plurality of components included in the image sensor200 (for example, a timing generator, a buffer, and a countercontroller).

The control signal that is transmitted from the sensor control circuit110 to the control register 210 may be transmitted via aninter-integrated circuit (I2C) bus, but the scope of the inventiveconcepts is not limited thereto.

The automatic gain controller 120 may determine a gain of an imagegenerated (“obtained”) at the image sensor 200 based on conversion oflight L that is detected (“received”) at an optoelectronic conversiondevice of the pixel array 260 of the image sensor 200 to cause theoptoelectronic conversion device of the pixel array 260 to generate oneor more electric signals. The gain may be determined based on theintensity of the detected light at the moment when the image isobtained. For example, when received light has a large intensity (forexample, when the image sensor 200 is in a bright place or outdoors), alarge number (“quantity”) of electrons may be generated by anoptoelectronic conversion device of the pixel array 260 of the imagesensor 200. Accordingly, even when the gain is amplified into a low gain(or x1), the gain may reach a saturation input of an analog-to-digitalconverter (ADC) 230. As another example, when received light has a smallintensity (for example, when the image sensor 200 is in a dark place ora darkroom), a small number of electrons may be generated by theoptoelectronic conversion device of the pixel array 260 of the imagesensor 200. Accordingly, when the gain is amplified into a high gain(e.g., x16), the gain may reach the saturation input of the ADC 230. Thedetermined gain may be used as a set value of a ramp 220. The automaticgain controller 120 may determine the gain by measuring the intensity ofperipheral light detected at the optoelectronic conversion device of thepixel array 260 by using auto exposure.

The digital signal processing circuit 130 may process the image datathat is generated at the image sensor 200 based on the electric signalsgenerated at the optoelectronic conversion device of the pixel array260. The digital signal processing circuit 130 may receive the imagedata from a buffer (for example, a buffer 280 of FIG. 2) included in theimage sensor 200 and may process the received image data. For example,the digital signal processing circuit 130 may process the image datasuch that a display (not shown) may display an image.

According to some example embodiments, the image sensor 200 may includethe control register 210, the ramp 220, and the ADC 230. The imagesensor 200 may include the pixel array 260. The pixel array 260 maygenerate an image based on light L being incident upon one or morepixels of the pixel array 260, and each pixel of the pixel array 260 mayinclude an optoelectronic conversion device. The pixels may generate animage based on one or more pixels generating an electric signal inresponse to light L being incident on the one or more pixels, where anoptoelectronic conversion device of the one or more pixels may absorb atleast some of the light L that is incident to the one or more pixels andconvert the absorbed light into an electric signal. Collectively, theelectric signals generated by the pixels of the pixel array 260 may beunderstood to be the image that is generated by the pixel array 260. Theimage sensor 200, including one or more elements thereof, including forexample some or all of the control register 210, ramp 220, ADC 230,buffer 280, and pixel array 260, may include processing circuitry(“image sensor processing circuitry”) such as hardware including logiccircuits; a hardware/software combination such as a processor executingsoftware; or a combination thereof. For example, the processingcircuitry more specifically may include, but is not limited to, acentral processing unit (CPU), an arithmetic logic unit (ALU), a digitalsignal processor, a microcomputer, a field programmable gate array(FPGA), a System-on-Chip (SoC), a programmable logic unit, amicroprocessor, application-specific integrated circuit (ASIC), etc. Insome example embodiments, one or more elements of the image sensor 200,including for example some or all of the control register 210, ramp 220,ADC 230, buffer 280, and pixel array 260, may be implemented byprocessing circuitry, such as described above as being included in theimage sensor 200, executing a program of instructions stored on a memorydevice and/or storage device. The image sensor processing circuitry mayinclude a memory storing a program of instructions and processingcircuitry configured to execute the program of instructions to implementthe functionality of some or all of the image sensor 200, including someor all of the control register 210, ramp 220, ADC 230, buffer 280, andpixel array 260.

The control register 210 may output (“transmit”) a control signal toeach of a ramp signal generator (not shown), a timing generator (notshown), a counter controller (not shown), and the buffer 280 of FIG. 2and may control operations thereof.

The ramp 220 may amplify a pixel output voltage of electric signalsgenerated by one or more pixels of the pixel array 260 based on light Lbeing incident on some or all of the pixel array 260 according to thevalue of the gain received from the image processor 100. For example,when an image has been obtained based on the image sensor 200 being in avery bright place (e.g., the light L has a relatively high intensity),the gain value may correspond to x1. In this case, the ramp 220 mayperform buffering. As another example, when an image is obtained basedon the image sensor 200 being in a very dark place (e.g., the light Lhas a relatively low intensity), the gain value may correspond to x16.In this case, the ramp 220 may amplify the pixel output voltage ofelectric signals generated by one or more pixels of the pixel array 260based on light L being incident on some or all of the pixel array 260 by16 times and apply the amplified pixel output voltage as an inputvoltage to the ADC 230, thereby reconstructing the image generated bythe pixel array 260 such that subjects may be easily distinguished fromeach other within the image.

The ADC 230 may convert an analog signal to a digital signal. Forexample, the ADC 230 may receive, from the ramp 220, an analog signalobtained by amplifying the pixel output voltage of electric signalsgenerated by one or more pixels of the pixel array 260 according to thevalue of the gain. The ADC 230 may convert the analog signal to adigital signal to thereby generate pixel data.

FIG. 2 is a block diagram of a structure of an image sensor according tosome example embodiments of the inventive concepts. The image sensor 200shown in FIG. 2 may be the image sensor 200 shown in FIG. 1. A repeateddescription given above with reference to FIG. 1 will be omitted.

Referring to FIG. 2, the image sensor 200 may include the controlregister 210 (also referred to as control register circuitry), a rowdecoder 240 (also referred to as row decoder circuitry), a row driver250 (also referred to as row driver circuitry), a pixel array 260, apixel load 270 (including pixel loads 270-1 to 270-n, also referred toas pixel load circuitry), the ramp 220 (also referred to as rampcircuitry), the ADC 230 (including ADCs 230-1 to 230-n, also referred toas ADC circuitry), and the buffer 280 (also referred to as buffercircuitry). A repeated description of the control register 210, the ramp220, and the ADC 230 described above with reference to FIG. 1 will beomitted.

The row driver 250, which may also be referred to as “row drivercircuitry”, may drive the pixel array 260 in units of rows. For example,the row driver 250 may generate a transmission control signal thatcontrols a transmit transistor 302 (see FIG. 3) of each pixel comprisingthe pixel array 260, a reset control signal that controls a resettransistor 303 of each pixel comprising the pixel array 260, and aselection control signal that controls a select transistor 305 of eachpixel comprising the pixel array 260.

The pixel array 260 may include a plurality of optoelectronic conversiondevices that are each included in a separate pixel of a plurality ofpixels 260-11 to 260-mn, where “m” and “n” are each a separate positiveinteger. Each of the optoelectronic conversion devices may include atleast one of a photodiode (PD), a photo gate, or a pinned photodiode(PDD). The pixels 260-11 to 260-mn of the pixel array 260, and thus theplurality of optoelectronic conversion devices included therein, may bearranged in a lattice shape including one or more rows of pixels and oneor more columns of pixels. The pixel array 260 may sense (“detect”)light by using the plurality of optoelectronic conversion devices of thepixels 260-11 to 260-mn and each optoelectronic conversion device of thepixels 260-11 to 260-mn may convert the light detected at the respectiveoptoelectronic conversion device of the pixels 260-11 to 260-mn (e.g.,light L that is incident on the respective optoelectronic conversiondevices) into a separate electrical signal to thereby generate an imagesignal, where the image signal may be referred to as an image generatedby the pixel array 260. The image signal may include the plurality ofelectrical signals generated simultaneously or near-simultaneously bythe separate optoelectronic conversion devices of the pixels 260-11 to260-mn of the pixel array based on detection of light at the separateoptoelectronic conversion devices of the pixels 260-11 to 260-mn.

As shown in FIG. 2, each separate pixel load 270-1 to 270-n is connectedto a separate column of pixels of the one or more columns of pixels ofthe pixel array 260. For example, as shown in FIGS. 2-3, pixel load270-1 is connected to column COL1 of pixels 260-11 to 260-m 1, and pixelload 270-n is connected to column COLn of pixels 260-1 n to 260-mn. Asfurther described below with reference to FIG. 3, each pixel load 270-1to 270-n includes a plurality of transistors serially connected to eachother.

FIG. 3 is an analog circuit diagram illustrating a pixel and a pixelload according to some example embodiments of the inventive concepts. Arepeated description given above with reference to FIG. 2 will beomitted. While the analog circuit diagram is shown for only pixel 260-11of FIG. 2, it will be understood that similar analog circuit diagramsmay be presented with regard to each of the pixels 260-11 to 260-mn.

Referring to FIG. 3, a pixel 260-11 may include an optoelectronicconversion device 301, a capacitor 306, and a plurality of transistors.According to some example embodiments, the plurality of transistors mayinclude the transmit transistor 302, the reset transistor 303, a drivetransistor (or source follower (SF)) 304, and the select transistor 305.According to some example embodiments, the optoelectronic conversiondevice 301 may include a PD, a photo gate, a PDD, or any combinationthereof.

The optoelectronic conversion device 301 may generate a photocharge thatvaries according to the intensity of incident light L sensed(“detected,” “received,” or the like) at the optoelectronic conversiondevice 301. The transmit transistor 302 may transmit the generatedphotocharge to the capacitor 306 according to a transmission controlsignal that is output to the gate of the transmit transistor 302 by therow driver 250.

The capacitor 306 may accumulate the photocharge received from thetransmit transistor 302. As the photocharge is accumulated, a node ofthe capacitor 306 may generate a voltage for driving the drivetransistor 304. The node, as shown in FIG. 3, may be referred to as afloating diffusion (FD) node. The drive transistor 304 may amplifyelectric potential of the FD node and transmit the amplified electricpotential to the select transistor 305. The select transistor 305 has adrain terminal connected to a source terminal of the drive transistor304 and may output an electric signal, also referred to herein as apixel signal, to a column COL1 connected to the pixel 260-11 accordingto a selection signal SEL output by the row driver 250 to the gate ofthe select transistor 305. The reset transistor 303 may reset the FDnode according to a reset control signal that is output by the rowdriver 250 to the gate of the reset transistor 303.

According to some example embodiments, the pixel 260-11 is illustratedas including four transistors, but the inventive concepts are notlimited thereto. According to some example embodiments, the pixel 260-11may have a 3Tr structure including three transistors (reset transistor,drive transistor, and select transistor), or a 5Tr structure includingfive transistors.

According to some example embodiments, the description of the pixel260-11 is equally applicable to a plurality of pixels 260-11 through260-mn included in the pixel array 260.

According to some example embodiments, a voltage component included in apixel output voltage, of electric signals (“pixel signals”) generated bya pixel, and generated due to thermal noise may be expressed as inEquation 1 below.

$\begin{matrix}{V_{n,{out}}^{2} = {\frac{2}{3} \times \left( {1 + \frac{g_{m2}}{g_{m1}}} \right) \times \frac{kT}{C_{L}}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

In Equation 1, k may correspond to a Boltzmann constant, T maycorrespond to an absolute temperature, C_(L) may correspond to acapacitance viewed from a pixel output node, g_(m1) may correspond to atransconductance value of a drive transistor, and g_(m2) may correspondto a transconductance value of the pixel load 270-1.

Referring to Equation 1, to reduce an output voltage, of a pixel signal,that is generated due to thermal noise, a transconductance g_(m2) of thepixel load 270-1 may be decreased. The transconductance g_(m2) of thepixel load 270-1 may be expressed using Equation 2 below.

$\begin{matrix}{g_{m2} = {\sqrt{2\beta \times I} = \sqrt{2 \times \mu_{n}C_{ox}\frac{W}{L} \times I}}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

In Equation 2, μ_(n) may correspond to the mobility of electrons, C_(ox)may correspond to a capacitance of a gate oxide layer, W may correspondto the width of a transistor channel, and L may correspond to the lengthof the transistor channel.

Referring to Equation 2, the transconductance g_(m2) of the pixel load270-1 may be proportional to a W/L ratio of a transistor. Accordingly,when the W/L ratio of the transistor is decreased, the transconductanceg_(m2) of the pixel load 270-1 may decrease and the voltage due tothermal noise within the pixel output voltage may decrease.

According to some example embodiments, the pixel load 270-1 may includean independent current source 307, a plurality of transistors, forexample, a first transistor 308, a second transistor 309, and a thirdtransistor 310, and a plurality of switches, for example, first andsecond switches 311 and 312.

According to some example embodiments, the independent current source307 may include a transistor. By applying a bias voltage to thetransistor, the independent current source 307 may be controlled tooutput a current of a certain magnitude. According to some exampleembodiments, the independent current source 307 is illustrated asincluding a single transistor, but example embodiments are not limitedthereto. The independent current source 307 may include a plurality ofcascaded transistors. By connecting the plurality of transistors to eachother, the independent current source 307 may operate as an idealcurrent source that outputs a current of a certain magnitude regardlessof an input voltage.

The first, second, and third transistors 308, 309, and 310 may beserially connected to each other to form (“define”) a stack structure.

According to some example embodiments, the pixel load 270-1 may includethe first and second switches 311 and 312. The first and second switches311 and 312 may be connected to the first through third transistors 308through 310 such that the first and second switches 311 and 312alternate with the first through third transistors 308 through 310. Asshown in FIG. 3, the switches 311 and 312 may be connected in parallelto separate, respective nodes N1 and N2 between neighboring (“adjacent”)transistors of the first, second, and third transistors 308, 309, and310. For example, the first switch 311 may be connected to a first nodeN1 between the first transistor 308 and the second transistor 309. Forexample, the second switch 312 may be connected to a second node N2between the second transistor 309 and the third transistor 310. Thefirst and second switches 311 and 312 may be connected to ground nodes,respectively.

According to some example embodiments, at least one switch of the firstand second switches 311 and 312 may receive a control signal from thecontrol register 210 and may be turned on or off (e.g., selectivelyactivated or inactivated). To reduce the W/L ratio of the pixel load270-1, the control register 210 may output a control signal instructingat least one of the first switch 311 or the second switch 312 to beinactivated. For example, when the first switch 311 is inactivated andthe second switch 312 is activated, the W/L ratio of the pixel load270-1, and thus the transconductance value of the pixel load 270-1, maybe halved (e.g., reduced by about ½). As another example, when both thefirst switch 311 and the second switch 312 are inactivated, the W/Lratio of the pixel load 270-1, and thus the transconductance value ofthe pixel load 270-1, may be reduced to ⅓ (e.g., reduced by about ⅔).

When the terms “about” or “substantially” are used in this specificationin connection with a numerical value, it is intended that the associatednumerical value include a tolerance of ±10% around the stated numericalvalue. When ranges are specified, the range includes all valuestherebetween such as increments of 0.1%.

According to some example embodiments, the image sensor 200 may furtherinclude a bias current circuit 400. The bias current circuit 400 maycorrespond to (e.g., may include) a current mirror circuit forgenerating a separate current that passes through the pixel load 270-1.Accordingly, it will be understood that the bias current circuit 400 maybe configured to generate a separate current that flows to the pixelload 270-1, separately from the current that flows to the pixel load270-1 from one or more pixels 260-11 to 260-m1.

The bias current circuit 400 may further include a plurality of switches401 and 402, also referred to herein as a plurality of additionalswitches. As shown in FIG. 3, the plurality of switches 401 and 402 mayform symmetry with (e.g., are in a symmetrical configuration with regardto) the first and second switches 311 and 312 connected to the pixelload 270-1. The plurality of switches 401 and 402 included in the biascurrent circuit 400 and the first and second switches 311 and 312connected to the pixel load 270-1 may be identically controlled, suchthat the plurality of switches 401 and 402 may be configured to beturned on or off, identically with the plurality of switches 311 and312. When the plurality of switches 401 and 402 included in the biascurrent circuit 400 are not identically controlled with the first andsecond switches 311 and 312 connected to the pixel load 270-1, a W/Lratio of the bias current circuit 400 does not change, whereas the W/Lratio of the pixel load 270-1 may be changed. The magnitude of a currentflowing in the pixel load 270-1 may be determined based on the W/Lratios of the bias current circuit 400 and the pixel load 270-1.Accordingly, the plurality of switches 401 and 402 included in the biascurrent circuit 400 are controlled identically as the first and secondswitches 311 and 312 connected to the pixel load 270-1 in order tomaintain the magnitude of the current flowing in the pixel load 270-1.

According to some example embodiments, the plurality of transistors arethree transistors, but embodiments are not limited thereto. According tosome example embodiments, the plurality of transistors may include ntransistors. According to some example embodiments to be describedlater, when the pixel load 270-1 includes n transistors, the magnitudeof the transconductance of the pixel load 270-1 may be scaled to 1/n,where “n” is a positive integer and may be a separate value from the “n”value of the “n” columns in the pixel array 260.

FIG. 4 is a flowchart of an operation of an image sensor according tosome example embodiments of the inventive concepts.

Referring to FIG. 4, in operation S110, the image sensor 200 may receivegain information from the image processor 100. The gain information mayindicate an intensity of the light L that is incident on some or all ofthe pixel array 260. The gain information may be received at the imagesensor at the same time or nearly the same as (e.g., concurrently with)the pixel array 260 of the image sensor 200 generating an image based onthe light L being incident on some or all of the pixel array 260. Inresponse to receiving a signal that requests image obtainment (“imagegeneration”), for example an image capture command generated by a userinterface (e.g., a button and/or touchscreen) based on user interactionwith the user interface, the image processor 100 may determine a gainvalue based on a measured intensity of light L by performing an autoexposure operation (e.g., processing images generated by the imagesensor 200 and/or sensor data generated by a light sensor device todetermine an intensity of light L). For example, the determined gainvalue may correspond to x1 to x16. When the image processor 100determines the gain value, the image processor 100 may transmit thedetermined gain value to the image sensor 200 as part of the gaininformation. The image sensor 200 may receive the gain information andmay determine the gain value based on the gain information and maychange the set value of the ramp 220 according to the determined gainvalue, concurrently with causing the pixel array 260 to generate animage. For example, when the predetermined gain value is x16, the ramp220 may amplify the pixel voltage by 16 times and may apply theamplified voltage as the input voltage of the ADC 230.

In operation S120, the image sensor 200 may control at least one switchof the plurality of switches (e.g., first switch 311 and second switch312) to be turned on/off to change an electrical path of a current thatpasses through a pixel load based on the generation of the image by thepixel array, based on the gain information. The image sensor 200 maydetermine a switch which is controlled to be turned on/off, by using thegain information. For example, when the gain information indicates again value of x16, light corresponding to an image obtainment time pointhas a very small intensity. When Vout is amplified 16 times, a thermalnoise component included in Vout is also amplified by 16 times, and thusreduction of thermal noise may be important. Accordingly, the imagesensor 200 may change an electrical path of the current flowing in thepixel load 270-1 and change the W/L ratio of the pixel load 270-1, byturning at least one of the plurality of switches on/off. Becausethermal noise is dependent upon the W/L ratio of the pixel load 270-1,the image sensor 200 may reduce thermal noise by reducing the W/L ratio.A detailed operation of controlling at least one switch to be turnedon/off will now be described with reference to FIG. 5.

FIG. 5 is a flowchart of a method of controlling an on/off operation ofa switch, according to some example embodiments of the inventiveconcepts. In more detail, FIG. 5 is a flowchart of operation S120 ofcontrolling at least one of the plurality of switches to be turnedon/off, based on the gain information.

Referring to FIG. 5, in operation S121, the image sensor 200 maydetermine whether the received gain value exceeds a first thresholdvalue. For example, the first threshold value may correspond to x5. Whenthe received gain value corresponds to x1 to x4, the image sensor 200does not amplify a pixel output by five times or greater, and thus maydetermine thermal noise in the pixel output to not be reduced. In otherwords, when the image sensor 200 amplifies the pixel output by 1 to 4times, performance degradation due to an ADC input voltage limited byreducing the W/L ratio may be greater than thermal noise reductionobtainable by reducing the W/L ratio. Accordingly, when the receivedgain value does not exceed the first critical value, the image sensor200 may terminate the procedure. Restated, in response to adetermination that the gain value does not exceed a first thresholdvalue, the image sensor 200 may bypass control of the at least oneswitch of switches 311 and 312 to be turned on/off, thereby refrainingfrom selectively activating or inactivating any of the switches based onthe gain value in relation to at least the first threshold value.

In operation S122, the image sensor 200 may inactivate the first switch311 and activate the second switch 312 in response to a determinationthat the gain value is greater than the first threshold value. Inoperation S121, when the received gain value exceeds the first thresholdvalue, thermal noise may be reduced by reducing the W/L ratio, and thusat least one of the plurality of switches may be controlled to be turnedon/off. For example, in response to a gain value exceeding the firstthreshold value, the control register 210 may output a control signalinactivating the first switch 311 and activating the second switch 312.When the first switch 311 is inactivated and the second switch 312 isactivated, the current flowing in the pixel load 270-1 may pass throughthe first transistor 308 and the second transistor 309 and then may flowto a ground node via the second switch 312. Because the first transistor308 and the second transistor 309 serially connected to each other tohave a stack structure are equivalent to a transistor of W/2 L, the W/Lratio of the pixel load 270-1 may be halved.

In operation S123, the image sensor 200 may determine whether thereceived gain value exceeds a second threshold value, in response to thedetermination that the gain value exceeds the first threshold value. Thesecond threshold value may be greater than the first threshold value.For example, the second threshold value may correspond to x10. When thereceived gain value corresponds to x5 to x9, the image sensor 200 doesnot amplify a pixel output value by ten times or greater, and thus maybypass additional reduction of the W/L ratio. In other words, when theimage sensor 200 amplifies the pixel output voltage by 5 to 9 times,performance degradation due to an ADC input voltage limited due to anadditionally reduced W/L ratio may be greater than thermal noisereduction obtainable by additionally reducing the W/L ratio.Accordingly, when the received gain value does not exceed the secondcritical value, the image sensor 200 may terminate the procedure.Restated, in response to a determination that the gain value is greaterthan the first threshold value and does not exceed a second thresholdvalue, the image sensor 200 may inactivate the first switch 311 andactivate the second switch 312.

In operation S124, the image sensor 200 may inactivate both the firstswitch 311 and the second switch 312 in response to a determination thatthe gain value is greater than the second threshold value. In operationS123, when the received gain value exceeds the second threshold value,thermal noise may be reduced by reducing the W/L ratio, and thus atleast one of the plurality of switches may be controlled to be turnedon/off. In other words, when the pixel output voltage is amplified by 10to 16 times, a thermal noise component included in the pixel outputvoltage is also amplified 10 to 16 times and output, and thus thermalnoise needs to be additionally reduced. For example, in response to again value exceeding the second threshold value, the control register210 may output a control signal inactivating the second switch 312. Whenthe second switch 312 is inactivated, because the first switch 311 andthe second switch 312 are inactivated, the current flowing in the pixelload 270-1 may pass through the first transistor 308, the secondtransistor 309, and the third transistor 310. Because the first, second,and third transistors 308, 309, and 310 serially connected to each otherto have a stack structure are equivalent to a transistor of W/3 L, theW/L ratio of the pixel load 270-1 may be reduced to ⅓.

FIG. 6A is a circuit diagram illustrating a flow of a pixel load currentaccording to control of a switch to be turned on/off, when a gain valuenot exceeding the first threshold value is received, according to someexample embodiments of the inventive concepts.

The image sensor 200 may receive gain information indicating the gainvalue not exceeding the first threshold value from the image processor100. For example, the gain value may correspond to x1 to x4. The imagesensor 200 may active the first switch 311 in response to the gaininformation. When the first switch 311 connected to a ground node isactivated, the pixel load current may have an electrical path includingthe first transistor 308 and the first switch 311. The electrical pathmay correspond to a bold line. In other words, the pixel load currentmay pass through the first transistor 308 and the first switch 311.Restated, the image sensor 200 may direct the current flowing in thepixel load 270-1 to follow an electrical path including the firsttransistor 308 and the first switch 311, based on the first switch 311being activated. Because the pixel load 270-1 through which the pixelload current passes is limited only by the first transistor 308, the W/Lratio of the pixel load 270-1 may correspond to the W/L ratio of thefirst transistor 308.

FIG. 6B is a circuit diagram illustrating a flow of a pixel load currentaccording to control of a switch to be turned on/off, when a gain valueexceeding the first threshold value and not exceeding the secondthreshold value is received, according to some example embodiments ofthe inventive concepts.

The image sensor 200 may receive gain information indicating the gainvalue exceeding the first threshold value and not exceeding the secondthreshold value from the image processor 100. For example, the gainvalue may correspond to x5 to x9. The image sensor 200 may inactivatethe first switch 311 and activate the second switch 312, in response tothe gain information. Because the first switch 311 in a stack structurewhere the plurality of transistors are formed is connected to an uppernode compared than the second switch 312, when the first switch 311 isactivated, the pixel load current may flow to a ground node via thefirst switch 311 regardless of whether the second switch 312 isactivated or inactivated. Accordingly, the image sensor 200 may changean electrical path such that the pixel load current passes through atleast two transistors connected to each other, by inactivating the firstswitch 311. The electrical path may correspond to a bold line. In otherwords, the pixel load current may pass through the first and secondtransistors 308 and 309 and the second switch 312. Restated, the imagesensor 200 may direct the current flowing in the pixel load 270-1 tofollow an electrical path including the first and second transistors 308and 309 and the second switch 312, based on the first switch 311 beinginactivated and the second switch 312 being activated. Because theelectrical path includes the first transistor 308 and the secondtransistor 309, the electrical path may be a circuit equivalent to asingle transistor having transconductance of the W/2 L ratio. Accordingto a halved W/L ratio, thermal noise in the pixel output voltage may bereduced.

FIG. 6C is a circuit diagram illustrating a flow of a pixel load currentaccording to control of a switch to be turned on/off, when a gain valueexceeding the second threshold value is received, according to someexample embodiments of the inventive concepts.

The image sensor 200 may receive gain information indicating the gainvalue exceeding the second threshold value from the image processor 100.For example, the gain value may correspond to x10 to x16. The imagesensor 200 may inactivate the first switch 311 and the second switch 312in response to the gain information. When the first switch 311 and thesecond switch 312 are inactivated, the pixel load current may flow to aground node connected to the third transistor 310. Accordingly, theimage sensor 200 may change an electrical path such that the pixel loadcurrent passes through at least three transistors, by inactivating thefirst and second switches 311 and 312. The electrical path maycorrespond to a bold line. The pixel load current may pass through thefirst, second, and third transistors 308, 309, and 310. Restated, theimage sensor 200 may direct the current flowing in the pixel load 270-1to follow an electrical path including each transistor of the firstthrough third transistors 308, 309, and 310, based on both the firstswitch 311 and the second switch 312 being inactivated. Because theelectrical path includes the first through third transistors 308 through310, the electrical path may be a circuit equivalent to a singletransistor having transconductance of the W/3 L ratio. According to aW/L ratio reduced to ⅓, thermal noise in the pixel output voltage may bereduced.

According to some example embodiments, the pixel load 270-1 isillustrated as having three transistors and two switches, butembodiments are not limited thereto. According to some exampleembodiments, the pixel load 270-1 may include n transistors and (n−1)switches. As shown in FIGS. 6A through 6C, the number of transistorsthrough which the pixel load current passes may be sequentiallyincreased by sequentially inactivating the switches from a switchconnected to an upper node to a switch connected to a lower node. As thenumber of transistors through which the pixel load current passessequentially increases, the W/L ratio of the pixel load 270-1 maydecrease in inverse proportion to the number of transistors. Forexample, the image sensor 200 may inactivate (n−1) switches, and thepixel load current may change an electrical path to pass through ntransistors. In this case, an equivalent circuit of the pixel load 270-1through which the pixel load current passes may correspond to a singletransistor having a W/nL ratio.

FIG. 7 is a block diagram of a computing system 700 including an imagesensor according to some example embodiments of the inventive concepts.

Referring to FIG. 7, the computing system 700 may include an imageprocessor 710, a memory device 720, a storage device 730, aninput/output (I/O) device 750, a power supply device 760, and an imagesensor 740. The image sensor 740 may include the image sensor 200according to some example embodiments of the inventive conceptsdescribed above with reference to FIGS. 1 through 6C. The imageprocessor 710 may include the image processor 100 according to someexample embodiments of the inventive concepts described above withreference to FIGS. 1 through 6C. Although not shown in FIG. 7, thecomputing system 700 may further include ports which are capable ofcommunicating with a video card, a sound card, a memory card, a USBdevice, or other electronic apparatuses.

The image processor 710 may execute specific calculations or specifictasks. The image processor 710 may include the image sensor 740according to some example embodiments of the inventive conceptsdescribed above with reference to FIGS. 1 through 6C. For example, theimage processor 710 may include a microprocessor or a central processingunit (CPU). The image processor 710 may communicate with the memorydevice 720, the storage device 730, and the I/O device 750 through anaddress bus, a control bus, and a data bus. For example, the imageprocessor 710 may be connected to an expansion bus such as a peripheralcomponent interconnect (PCI) bus. When the image processor 710 receivesa digital zoom command from a host or the like, the image processor 710may output zoom information according to the digital zoom command to theimage sensor 740 via a bus.

The memory device 720 may store data necessary for operations of thecomputing system 700. For example, the memory device 720 may beimplemented using DRAM, mobile DRAM, SRAM, or a non-volatile memory.

A chip of the DRAM, the mobile DRAM, the SRAM, and the non-volatilememory may be mounted by using various types of packages. For example,the chip may be packaged as a package, such as a package on package(POP), ball grid arrays (BGAs), chip scale packages (CSPs), a plasticleaded chip carrier (PLCC), a plastic dual in-line package (PDIP), a diein waffle pack, a die in wafer form, a chip on board (COB), a ceramicdual in-line package (CERDIP), or a plastic metric quad flat pack(MQFP).

The storage device 730 may include a solid state drive (SSD), a harddisk drive (HDD), a CD-ROM, and the like. The I/O device 750 may includean input device, such as a keyboard, a keypad, or a mouse, and outputunits, such as a printer and a display. The power supply device 760 maysupply an operating voltage necessary for operations of the computingsystem 700.

As shown in FIG. 7, the image sensor 740 may be connected to the imageprocessor 710 via buses or another communication link and thus performcommunication with the image processor 710. According to embodiments ofthe inventive concepts, when the image sensor 740 receives gaininformation from the image processor 710, the image sensor 740 maychange a transconductance value of a pixel load by turning at least oneof a plurality of switches on/off, based on a comparison between thefirst threshold value and the second threshold value, thereby reducingthermal noise. The image sensor 740 and the image processor 710 may beintegrated into a single chip, or may be integrated into differentchips. The computing system 700 may be interpreted as any computingsystem using an image sensor. For example, the computing system 700 mayinclude a digital camera, a mobile telephone, a personal digitalassistant (PDA), a portable multimedia player (PMP), a smartphone, and atablet PC.

The inventive concepts have been particularly shown and described withreference to example embodiments thereof. The terminology used herein isfor the purpose of describing example embodiments only and is notintended to be limiting of the inventive concepts. Therefore, it will beunderstood by those skilled in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the inventive concepts as defined by the appended claims.

What is claimed is:
 1. An image sensor, comprising: a pixel arrayincluding a plurality of pixels, the plurality of pixels arranged in oneor more rows of pixels and one or more columns of pixels, the pixelarray configured to generate an image based on light being incident toone or more pixels of the plurality of pixels; pixel load circuitryconnected to one column of pixels of the one or more columns of pixels,the pixel load circuitry including a plurality of transistors seriallyconnected to each other; and a plurality of switches connected inparallel to separate, respective nodes between adjacent transistors ofthe plurality of transistors, wherein the image sensor includes imagesensor processing circuitry configured to receive, from image processorcircuitry, gain information indicating an intensity of the lightconcurrently with the pixel array generating the image, and control atleast one switch of the plurality of switches to be turned on/off tochange an electrical path of a current that passes through the pixelload circuitry, based on the pixel array generating the image, based onthe gain information.
 2. The image sensor of claim 1, wherein theplurality of transistors are serially connected to each other to definea stack structure.
 3. The image sensor of claim 1, wherein the pluralityof switches include a first switch and a second switch, and theplurality of transistors include a first transistor, a secondtransistor, and a third transistor.
 4. The image sensor of claim 3,wherein the first switch is connected to a first node between the firsttransistor and the second transistor, and the second switch is connectedto a second node between the second transistor and the third transistor.5. The image sensor of claim 4, wherein the image sensor is configuredto identify a gain value, based on the gain information, bypass controlof the at least one switch to be turned on/off in response to adetermination that the gain value does not exceed a first thresholdvalue, inactivate the first switch and activate the second switch inresponse to a determination that the gain value is greater than thefirst threshold value and does not exceed a second threshold value, andinactivate both the first switch and the second switch in response to adetermination that the gain value is greater than the second thresholdvalue.
 6. The image sensor of claim 5, wherein the image sensorprocessing circuitry is configured to direct the current flowing in thepixel load circuitry to follow an electrical path including the firsttransistor and the first switch, based on the first switch beingactivated, direct the current flowing in the pixel load to follow anelectrical path including the first and second transistors and thesecond switch, based on the first switch being inactivated and thesecond switch being activated, and direct the current flowing in thepixel load to follow an electrical path including each transistor of thefirst through third transistors, based on both the first switch and thesecond switch being inactivated.
 7. The image sensor of claim 5, whereinthe image sensor processing circuitry is configured to cause atransconductance value of the pixel load circuitry to be reduced byabout ½ based on the first switch being inactivated and the secondswitch being activated, and the image sensor processing circuitry isconfigured to cause the transconductance value of the pixel load to bereduced by about ⅔ based on both the first switch and the second switchbeing inactivated.
 8. The image sensor of claim 1, further comprising: abias current circuit configured to generate a separate current thatflows to the pixel load circuitry.
 9. The image sensor of claim 8,wherein the bias current circuit includes a current mirror circuit. 10.The image sensor of claim 9, wherein the bias current circuit includes aplurality of additional switches that are in a symmetrical configurationwith regard to the plurality of switches, and the plurality ofadditional switches are configured to be turned on or off, identicallywith the plurality of switches.
 11. A method of operating an imagesensor, the method comprising: receiving, from image processorcircuitry, gain information indicating an intensity of lightconcurrently with generation of an image at a pixel array of the imagesensor based on the light being incident to one or more pixels of pixelarray; and controlling at least one switch of a plurality of switches ofthe image sensor to be turned on/off to change an electrical path of acurrent that passes through pixel load circuitry of the image sensorbased on the pixel array generating the image, based on the gaininformation, wherein the plurality of switches are connected in parallelto separate, respective nodes between adjacent transistors among aplurality of transistors of the pixel load circuitry that are seriallyconnected to each other.
 12. The method of claim 11, wherein thecontrolling of the at least one switch to be turned on/off includesidentifying a gain value, based on the gain information, and determiningwhether the gain value exceeds a first threshold value.
 13. The methodof claim 12, further comprising: bypassing control of the at least oneswitch to be turned on/off, based on a determination that the gain valuedoes not exceed the first threshold value.
 14. The method of claim 12,further comprising: inactivating a first switch of the plurality ofswitches and activating a second switch of the plurality of switches,based on a determination that the gain value exceeds the first thresholdvalue, wherein the first switch is connected to a first node between afirst transistor and a second transistor of the plurality oftransistors, wherein the second switch is connected to a second nodebetween the second transistor and a third transistor of the plurality oftransistors.
 15. The method of claim 14, further comprising: determiningwhether the gain value exceeds a second threshold value that is greaterthan the first threshold value, in response to the determination thatthe gain value exceeds the first threshold value, and inactivating boththe first switch and the second switch, in response to the determinationthat the gain value exceeds the second threshold value.
 16. The methodof claim 15, wherein a transconductance value of the pixel loadcircuitry is reduced by about ½ in response to the first switch beinginactivated and the second switch being activated, and thetransconductance value of the pixel load is reduced by about ⅔ inresponse to both the first switch and the second switch beinginactivated.
 17. The method of claim 15, wherein the current that passesthrough the pixel load circuitry is transmitted along an electrical pathincluding the first transistor and the first switch in response to thefirst switch being activated.
 18. The method of claim 15, wherein thecurrent that passes through the pixel load circuitry is transmittedalong an electrical path including the first and second transistors andthe second switch in response to the first switch being inactivated andthe second switch being activated.
 19. The method of claim 15, whereinthe current that passes through the pixel load circuitry is transmittedalong an electrical path including the first through third transistorsin response to both the first switch and the second switch beinginactivated.
 20. An electronic device comprising: image processorcircuitry and an image sensor, wherein the image processor circuitry isconfigured to transmit, to the image sensor, gain information indicatingan intensity of light concurrently with the image sensor generating animage at a pixel array of the image sensor based on the light beingincident to one or more pixels of pixel array; and the image sensorincludes image sensor processing circuitry configured to control atleast one switch of a plurality of switches to be turned on/off tochange an electrical path of a current that passes through pixel loadcircuitry of the image sensor based on the pixel array generating theimage, based on the gain information.